This invention relates generally to medical instruments and procedures, and more specifically to a treatment process and apparatus for the disease known as atherosclerosis.
Of the various forms of arteriosclerosis, in which the internal passageway of an artery becomes restricted or blocked, the most common and important is known as atherosclerosis. This disease is characterized by intimal thickening resulting from an accumulation of lipids. These localized accumulations tend to occur in coronary, cerebral, and peripheral arteries, and complications of the disease are the major causes of death in this country. One-third of deaths reported are classified as caused by arteriosclerotic and degenerative heart disease, and the third most common cause after heart disease and cancer is cerebral vascular disease.
A number of reconstructive surgical procedures have been developed to relieve the occlusion resulting from atherosclerosis. These include resection with graft replacement, thrombo-endarectomy, and by-pass graft. However, these procedures necessarily involve a number of disadvantages. Many depend on removing an artery or vein from one part of the body for use in replacement of the occluded artery. Finding such an artery or vein which is both in a reasonably healthy condition and available for removal without replacement itself can be difficult. In a significant number of cases, arterial surgery cannot be conducted due to a condition commonly known as poor run-off, which refers to a lack of blood supply to the reconstruction site as a result of occlusion of arteries remote from the site.
Several procedures and apparatus have, therefore, been developed in the past several years to reduce or eliminate the need for by-pass or replacement surgery by re-establishing a lumen of proper diameter within the occluded artery. One such procedure is known as translumenal angioplasty in which a balloon catheter with a a sausage-shaped balloon of high tensile strength and low elasticity is inserted to the point of occlusion. The balloon tip is positioned within the remaining restricted lumen surrounded by the occlusive material. The balloon, when inflated to a pressure such as four atmospheres, becomes sufficiently rigid to dilate the intima and re-establish a full lumen. There are a significant number of occlusions which cannot be dilated in this fashion because the intima has achieved sufficient rigidity to resist the dilating pressure exerted by the balloon.
U.S. Pat. No. 3,886,943 discloses a surgical knife for removal of occlusive material from the intima of an arterial wall. The curved knife blade is mounted on a long rod with a handle for manipulation of the blade by the physician. Since the blade is necessarily of a fixed diameter, it cannot be used effectively in arteries smaller than the diameter, which requires the physician to retain on hand a number of blade of different diameters. Furthermore, the invention requires surgery to reach the approximate site of occlusion, since the blade rod is of limited length and is rigid.
U.S. Pat. No. 4,058,126 discloses a spring-loaded impact hammer and clamp for fracture of intimal occlusions by application of a sudden blow to the outside of the artery. Since the intima has become brittle as a result of occlusive structure, while the remaining layers of arterial tissue remain flexible, a sudden blow of proper strength will fracture the occlusive material without damaging the artery. The fractured material is then carried away from the site by the bloodstream and is disposed in normal cardiovascular processes. While this device can act on arteries of a broad range of diameters, it nonetheless requires access by the physician to the exterior of the artery by surgery.
U.S. Pat. No. 3,811,446 discloses a catheter with vibrating tip for insertion in the occlusive site by surgical access. This system also takes advantage of the fact that the exterior arterial layers are more elastic than the occlusive material. The tip of the catheter is a wire loop which is vibrated rapidly by a motor-drive outside the body. The repeated impact of the vibrated wire loop causes the exterior arterial layers to stretch and separate from the rigid, non-elastic occlusive material. The occlusive material is then removed from the artery and the artery is surgically closed. This device also has the disadvantage of requiring surgery to give access to the site of occlusion.
U.S. Pat. No. 4,273,128 discloses a balloon catheter combined with a knife tip for removal of occlusive material. The tip of the catheter is a flexible probe of minimum diameter, which is followed by the knife blades and then by the balloon. The knife blades are semi-circular and radiate outward from the central axis of the device. When the leading probe has reached the occlusion site, the device is pressed forward and the knife blades are rotated to drill through the central portion of the occlusion, thereby removing enough brittle material so that the balloon may be positioned within the occlusion and expand to dilate the site as described above. While this system offers the advantage of treatment by catheterization rather than the more traumatic surgery, it exposes the entire length of the artery, from insertion to occlusion, to the knife blades. Since an artery may normally follow a non-linear path, this entails some danger to the patient. Furthermore, since these blade are also of fixed diameter, blades of differing diameters are required to fit within arteries of different diameters.
Thus it can be seen that the need exists in the art for a method and apparatus for treatment of atherosclerotic conditions which does not involve the necessity of surgery, and which allows the physician to treat arteries of any diameter with one and the same apparatus. The new system should also avoid exposure of the arterial lumen to knife blades operated remotely.